1. Field of the Invention
The present invention relates to a flow rate control apparatus which attenuates the pulsation of a pressure fluid flowing through a fluid passage and which is capable of controlling the flow rate of the pressure fluid highly accurately.
2. Description of the Related Art
FIG. 10 shows a conventional flow rate control system for controlling the flow rate of a fluid flowing through a fluid passage.
The flow rate control system 1 comprises a pump 3 which pumps and feeds a pressure fluid stored in a tank 2, an opening/closing valve 5 which is connected on the downstream side of the pump 3 via a tube passage 4 and which opens/closes a fluid passage for the pressure fluid fed from the pump 3, and a flow rate control valve 7 which is connected on the downstream side of the opening/closing valve 5 via a tube passage 6 and which controls the flow rate of the pressure fluid flowing through the fluid passage.
A flow rate sensor 8, which detects the flow rate of the pressure fluid flowing through the fluid passage, is provided on the downstream side of the flow rate control valve 7. The flow rate of the pressure fluid flowing through the fluid passage is indicated on an indicator 9 based on a detection signal supplied from the flow rate sensor 8.
An electropneumatic regulator 11 is connected to the flow rate control valve 7 via a tube passage 12 for regulating the pressure of the air supplied from a compressed air supply source 10 to provide a predetermined pilot pressure for a pilot chamber of the flow rate control valve 7. The electropneumatic regulator 11 controls the air supplied from the compressed air supply source 10 to have a predetermined pressure based on a control signal from a controller 13 so that the pressure is provided as a pilot pressure.
The operation of the conventional flow rate control system 1 described above will be schematically explained. The pressure fluid is stored in the tank 2 and is fed by the pump 3. The pressure fluid is introduced into the flow rate control valve 7 when the opening/closing valve 5 is opened. The pilot pressure is regulated to have the predetermined pressure by the electropneumatic regulator 11, and is introduced into the pilot chamber of the flow rate control valve 7. The valve opening degree of an unillustrated valve plug is controlled in the flow rate control valve 7 by balancing the pilot pressure introduced into the pilot chamber and the pressure (primary pressure) of the pressure fluid supplied from the opening/closing valve 5.
Therefore, the valve opening degree of the valve plug is adjusted in the flow rate control valve 7 by balancing the pilot pressure controlled based on the control signal from the controller 13 and the primary pressure of the pressure fluid supplied from the opening/closing valve 5. The pressure fluid is provided after being controlled to have the flow rate corresponding to the valve opening degree of the valve plug.
The flow rate of the pressure fluid from the flow rate control valve 7 is detected by the flow rate sensor 8, and the detected flow rate is indicated on the indicator 9.
However, in the conventional flow rate control system 1 described above, the valve opening degree of the flow rate control valve 7 is controlled by the pneumatic pressure (pilot pressure) from the electropneumatic regulator 11. Therefore, some dispersion appears in the flow rate due to the delay of response when the valve opening degree of the unillustrated valve plug is controlled, and it is difficult to stably control the flow rate.
Further, in the conventional flow rate control system 1, the piping passages between the fluid-operated apparatuses including, for example, the opening/closing valve 5, the flow rate control valve 7, and the electropneumatic regulator 11 are connected by the tube passages 4, 6. Therefore, piping operation is complicated, installation area is increased, and working space is increased.
Furthermore, in the conventional flow rate control system 1, some pressure fluctuation such as pulsation appears in the pressure fluid supplied from the opening/closing valve 5, for example, resulting from the feeding operation of the pump. Therefore, it is difficult to stably control the flow rate by the flow rate control valve 7.